I. Technical Field
This invention pertains to telecommunications, and particularly to transmission of frames of information in wireless telecommunications.
II. Related Art and Other Considerations
In a typical cellular radio system, wireless terminals (also known as mobile terminals, mobile stations, and mobile user equipment units (UEs)) communicate via base stations of a radio access network (RAN) to one or more core networks. The wireless terminals (WT) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network. The base station, e.g., a radio base station (RBS), is in some networks also called “NodeB” or “B node”. The base stations communicate over the air interface (e.g., radio frequencies) with the wireless terminals which are within range of the base stations.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UTRAN is essentially a radio access network providing wideband code division multiple access for user equipment units (UEs). The radio access network in a UMTS network covers a geographical area which is divided into cells, each cell being served by a base station. Base stations may be connected to other elements in a UMTS type network such as a radio network controller (RNC). The Third Generation Partnership Project (3GPP or “3G”) has undertaken to evolve further the predecessor technologies, e.g., GSM-based and/or second generation (“2G”) radio access network technologies.
The IEEE 802.16 Working Group on Broadband Wireless Access Standards develops formal specifications for the global deployment of broadband Wireless Metropolitan Area Networks. Although the 802.16 family of standards is officially called WirelessMAN, it has been dubbed WiMAX” (from “Worldwide Interoperability for Microwave Access”) by an industry group called the WiMAX Forum.
IEEE 802.16e-2005 (formerly known as IEEE 802.16e) is in the lineage of the specification family and addresses mobility by implementing, e.g., a number of enhancements including better support for Quality of Service and the use of Scalable OFDMA. In general, the 802.16 standards essentially standardize two aspects of the air interface—the physical layer (PHY) and the Media Access Control layer (MAC).
Concerning the physical layer, IEEE 802.16e uses scalable OFDMA to carry data, supporting channel bandwidths of between 1.25 MHz and 20 MHz, with up to 2048 sub-carriers. IEEE 802.16e supports adaptive modulation and coding, so that in conditions of good signal, a highly efficient 64 QAM coding scheme is used, whereas where the signal is poorer, a more robust BPSK coding mechanism is used. In intermediate conditions, 16 QAM and QPSK can also be employed. Other physical layer features include support for Multiple-in Multiple-out (MIMO) antennas in order to provide good performance in NLOS (Non-line-of-sight) environments and Hybrid automatic repeat request (HARQ) for good error correction performance.
In terms of Media Access Control layer (MAC), the IEEE 802.16e encompasses a number of convergence sublayers which describe how wireline technologies such as Ethernet, ATM and IP are encapsulated on the air interface, and how data is classified, etc. It also describes how secure communications are delivered, by using secure key exchange during authentication, and encryption during data transfer. Further features of the MAC layer include power saving mechanisms (using Sleep Mode and Idle Mode) and handover mechanisms.
The IEEE standard 802.16m is intended to be an evolution of IEEE standard 802.16e with the aim of higher data rates and lower latency. There is a requirement for backward compatibility between IEEE standard 802.16m and its IEEE standard 802.16e predecessor. Yet, the frame structure of IEEE standard 802.16e poses problems for backward compatibility.
The frame structure for IEEE standard 802.16e is shown in FIG. 1. The frame length for IEEE standard 802.16e is 5 ms, and uses time division duplex (TDD). The preamble is used by mobile stations to synchronize to the downlink (DL), and the DL-MAP and UL-MAP messages that occur just following the preamble give allocation information to the mobile stations on the downlink and the uplink. Examples of downlink and uplink allocations are shown in FIG. 1. The transmit transition gap (TTG) and the receive transition gap (RTG) are gaps used for the mobile station to switch from receive to transmit and vice versa.
As mentioned above, presently WiMAX utilizes orthogonal frequency division multiple access (OFDMA). Like OFDM, OFDMA transmits a data stream by dividing the data stream over several narrow band sub-carriers (e.g. 512, 1024 or even more depending on the overall available bandwidth [e.g., 5, 10, 20 MHz] of the channel) which are transmitted simultaneously. The sub-carriers are divided into groups of sub-carriers, each group also being referred to as a sub-channel. The sub-carriers that form a sub-channel need not be adjacent. As many bits are transported in parallel, the transmission speed on each sub carrier can be much lower than the overall resulting data rate. This is important in a practical radio environment in order to minimize effect of multipath fading created by slightly different arrival times of the signal from different directions.
With all of its advantages, WiMAX mobile does have a number of problems. Among its problems is the fact that the use of orthogonal frequency division multiple access (OFDMA), with its inherent large peak to average power ratio (PAPR), in the uplink makes user terminals complex and expensive.
There are some current solutions which seek to solve such OFDMA-related/caused problems. As one example, the use of single carrier frequency division multiple access (SC-FDMA) modulation as in long term evolution (LTE) has been proposed. Single Carrier Frequency Division Multiple Access (SC-FDMA) also transmits data over the air interface in many sub-carriers but adds an additional processing step (using, e.g., a Fast Fourier Transformation (FFT) function) for spreading the information of each bit over all the sub-carriers. SC-FDMA is sometimes also referred to as “FFT spread OFDM”.
As used herein, “SC-FDMA” encompasses but is not limited to SC-FDMA as described in 3GPP TS 36.300 V8.2.0 (2007-09) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 8) and 3GPP TS 36.211 V8.0.0 (2007-09) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8) and can also be referred to as DFTS-OFDM.
Use of technology such as SC-FDMA modulation in a WiMAX system having the currently envisioned frame structure may inhibit or even be antithetical to backward compatibility.
What is needed, therefore, and an object of the present invention, is one or more of method, apparatus, and techniques to introduce these features in a backwards-compatible manner.